If you had one Al, how many Cl would you need to make a correct
compound?

An ionic compound must be neutral, which means the positive and negative charges must be equal. So we need three chloride ions to bond with one aluminum ion, and the formula for aluminum chloride is AlCl3.

Hope it helps ps have a great day! :) (taken from google)

The offspring will be blood type aa, bb, ab and oo or i